Methods for the preparation of films of high temperature superconductor (HTS) materials on various substrates are well known. These methods have been instrumental for converting HTS materials into tapes and wires, a necessary step in the effort for integrating these materials as wiring into conventional electrical grid systems and devices. Several companies produce HTS wires and tapes of various lengths.
The first HTS tapes suffered from unacceptably low critical current densities, a problem caused by poor alignment of grains in the HTS film or coating with grains of the substrate. Several techniques have therefore been developed to fabricate wires or tapes wherein grain alignment is produced. Of particular note is epitaxial growth of superconductors on such ordered substrates as the Rolling-Assisted-Biaxially-Textured-Substrates (RABiTS). RABiTS substrates typically include a textured metal underlayer (for example, nickel or nickel alloy) and an epitaxial buffer layer (for example, Y2O3 and/or yttria-stabilized zirconia, YSZ). The development, preparation, and application of RABiTS is disclosed in several references and patents, including, for example, U.S. Pat. Nos. 7,087,113, 5,739,086, 5,741,377, 5,898,020, 5,958,599, and 5,944,966. Epitaxial superconductors on biaxially-textured substrates have significantly improved critical current densities of HTS tapes, and thus, improved suitability for commercial applications.
However, a well-known problem of HTS tapes and wires to which much research has been directed is the dissipation in critical current density (typically expressed as Jc) of the superconductor film when the superconductor film is exposed to an external magnetic field. Since external magnetic fields (typically as high as 5 Tesla, or higher) are prevalent in most commercial and industrial applications, there has been a significant effort in incorporating design features into the superconductor film that mitigate these current density losses. One particularly promising method has been to introduce structural defects (i.e., pinning defects) into the superconductor film. The pinning defects have been found to significantly reduce current density losses in superconductor films in the presence of an external magnetic field.
Though physical methods (e.g., by laser scribing or photolithographic patterning) and chemical doping (e.g., with BaZrO3) have been utilized to introduce pinning defects into the superconductor film, recent research has focused on introducing such defects into superconducting films by growing superconducting films epitaxially on substrates possessing microstructural defects (e.g., phase-separated components). However, the common techniques currently capable of producing such phase-separated substrates (e.g., physical vapor deposition (PVD), pulsed laser deposition (PLD), molecular beam epitaxy (MBE), and atomic layer deposition (ALD)), possess the significant drawbacks of being non-scalable, cost prohibitive, and industrially inefficient (i.e., typically of low throughput).
There is a need for a method capable of producing epitaxial layers of phase-separated substrates in a high-throughput manner and within the time and cost constraints that would make the method feasible for use on an industrial scale. The method would preferably be integratable with current HTS tape production methods. By producing improved HTS tapes and wires cost-effectively on a large scale, such a method could hasten the adoption of superconducting wiring in a variety of applications, and make a superconducting wiring infrastructure more realizable and achievable.